The present invention relates to an insert casting component having an outer surface insert cast in cast metal, a method for forming a coating on the insert casting component, a cylinder block using the insert casting component as a cylinder liner, and a method of manufacturing the same.
Insert casting is performed to integrate, for example, a cylinder liner, which serves as an insert casting component, with a cylinder block in cast metal. The cylinder liner forms a cylinder bore in the cylinder block. It is important that a strong bonding force be produced between the outer surface of the cylinder liner and the cylinder block to maintain the roundness of the cylinder bore.
It is also extremely important that the properties of the outer surface of the cylinder liner be adjusted to produce a strong bonding force between the outer surface of the cylinder liner and the cylinder block. Accordingly, Japanese Laid-Open Utility Model Publication No. 53-163405 proposes coating the outer surface of the cylinder liner with a sprayed layer. In Japanese Laid-Open Utility Model Publication No. 53-163405, grains of metal are adhered in an irregular manner to the outer surface of the cylinder liner to form pits in the outer surface. During casting, liquid metal flows into the pits. This produces an anchoring effect that generates a strong bonding force between the outer surface of the cylinder liner and the cylinder block.
Japanese Laid-Open Patent Publication No. 2003-53508 proposes metallurgical application of a coating of a low melting point material to the outer surface of a cylinder liner by performing shot peening, plasma spray, or the like. This resists the formation of an oxidized film on the outer surface of the cylinder liner and improves adhesion between the outer surface of the cylinder liner and the cylinder block.
Japanese Laid-Open Patent Publication No. 2003-120414 proposes the formation of an active layer of aluminum alloy on the outer surface of a cylinder liner at the top dead point region and the bottom dead point region of a piston. This bonds the cylinder liner with metal to a crankcase.
Internal combustion engines have become lighter while increasing output. As a result, the intervals between cylinder bores have become narrower. Thus, for a cylinder block formed by insert casting a cylinder liner with cast metal, it is required that the bonding force between the cylinder liner and the cylinder block be further increased.
In Japanese Laid-Open Utility Model Publication No. 53-163405, recesses are formed in the outer surface of a cylinder liner to receive liquid metal during casting. Thus, part of the cylinder block is anchored in the recesses to the outer surface of the cylinder liner. However, since liquid metal only contacts the outer surface of the cylinder liner, there is a limit to the anchoring with the recesses in the outer surface of the cylinder liner. Thus, sufficient bonding force cannot be obtained with only the recesses in the outer surface of the cylinder liner.
In Japanese Laid-Open Patent Publication No. 2003-53508, a coating having a low melting point is applied to the outer surface of the cylinder liner. During casting, the coating contacts liquid metal. This produces a thermal effect and fuses the coating thereby obtaining satisfactory metallic bonding. However, the entire coating is entirely formed of only low melting point material. Although this improves thermal conductivity, sufficient bonding force just through contact of liquid metal with a homogeneous film.
In Japanese Laid-Open Patent Publication No. 2003-120414, an active layer having a melting point lower than that of the cylinder liner is formed. However, the active layer is formed from a homogeneous aluminum alloy. Thus, sufficient bonding force cannot be obtained just by melting the surface of the active layer.